The number of belt CVTs mounted in an automobile has since gradually increased for improvement in automotive fuel economy. With a strong social demand for CO2 gas emission control in the background, progress has lately been made in technological development toward further enhancement in efficiency of the belt CVT. With the belt CVT, a multitude of block-like components bundled up with a multi-layer metal belt, called an element, are sandwiched between two pulleys opposing each other, and power transmission is effected by the agency of a frictional force generated upon slidable movement occurring between the element and the pulleys. Accordingly, power transmission efficiency can be enhanced by increasing a friction coefficient between the pulley and the element
On the other hand, from the viewpoint of stabilizing slidable movement between the pulley and the element, there is the need for enhancement in abrasion resistances of the pulley and the element, respectively, and if a wear depth is large (poor in abrasion resistance), gradual deterioration in power transmission performance is anticipated even in the case of high friction (high in friction coefficient). Conversely, even if abrasion resistance is excellent, the same can be said in the case of low friction (low in friction coefficient).
In order to cope with such a problem as described, a technology for improving friction/wear properties has since been proposed. For example, as described in Patent document 1, there has been proposed a method comprising the steps of enhancing discharge characteristic of an lubricating oil by controlling surface roughness of a pulley to a given state, thereby reducing a thickness of an oil film formed between the pulley and an element, and raising an inter-metallic contact ratio to thereby increase a friction coefficient.
Further, in Patent documents 2, and 3, respectively, there has been disclosed a method for improving tumbling fatigue strength by providing contact surfaces of an pulley, and so forth with high compressive stress by applying shot-blasting, and improving abrasion resistance of sliding faces to thereby maintain a high friction coefficient.
Still further, for the pulley of this kind, use has since been made of an alloy steel for machine construction, such as SCr420H, and so forth, containing Mn, and Cr, in given amounts, respectively. Further, in Patent documents 4, 5, and 6, respectively, there has been proposed a carburized steel for use in a pulley, chemical composition thereof, including C, Si, Mn, and so forth, being adjusted to thereby improve mechanical properties such as fatigue strength, and so forth.    Patent document 1: JP-A No. 2002-213580    Patent document 2: JP-A No. 5 (1993)-157146    Patent document 3: JP-A No. 2000-130527    Patent document 4: JP-A No. 2000-160288    Patent document 5: JP-A No. 2005-200667    Patent document 6: JP-A No. 2006-28568